A halogen gas is used in an etching step in the fabrication of semiconductor devices. In order to protect an etching apparatus from corrosion by halogen gas, the inner side of the etching apparatus is usually coated with a highly anti-corrosive substance by, for example, thermal spraying. It has also been practiced to construct the internal parts of the apparatus from a sintered body of a highly anti-corrosive substance. Materials containing a rare earth element are often used as such a substance.
Materials containing a rare earth element for use as a thermal spray material are usually granulated into flowable granules. Raw materials for use as a sintering material are also granulated.
Among known thermal spray materials containing a rare earth element is a particulate rare earth oxyfluoride having an aspect ratio of 2 or smaller, an average particle size of 10 to 100 μm, and a bulk density of 0.8 to 2 g/cm3 and containing not more than 0.5% by mass of carbon and 3 to 15% by mass of oxygen. It is known that this thermal spray material can be prepared by granulation (see Patent Literature 1 below).
There is a method for producing rare earth oxide solid spherical particles comprising dispersing a rare earth oxide powder with an average particle size of 1 μm or smaller in water to prepare a slurry and adding an organic acid salt to thereto, followed by spray drying. It is known that the resulting rare earth solid spherical particles are useful to make a sintered body (see Patent Literature 2).
A known method for producing a rare earth fluoride sintered body having high resistance to corrosion by a halogen-based plasma comprises molding a Group 3A metal fluoride powder containing a total of not more than 100 ppm of metal elements other than the group 3A metal and having an average particle size of 30 μm or smaller to form a green body of prescribed shape and firing the green body to a relative density of 95% or higher (see Paras. [0025]-[0028] of Patent Literature 3).
An oxyhalide-based member is disclosed, the part of which that is to be exposed to a halogen (e.g., fluorine or chlorine) corrosive gas or a halogen-based plasma is a sintered body represented by general formula: LnZ3−2xOx (wherein Ln is one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; Z is one or more of F, Cl, Br, and I; and 0<X<1) (see Para. [0005] of Patent Literature 4).